The inventor of the present application has invented many techniques in which a dot pattern on such a medium on which the dot pattern and an image are superimposed and printed is read in order to output information.
Japanese Published Unexamined Patent Application No. 2007-79993 discloses an invention in which a dot pattern and a map are superimposed and printed, and, by reading the dot pattern on the map, information corresponding to the coordinates on the map is output.
Japanese Published Examined Patent Application No. 4042065 discloses an invention in which a dot pattern and a drawing pattern of a keyboard for a personal computer are superimposed and printed, and, by reading the dot pattern on a key of the keyboard, an input instruction corresponding to the key is performed to the personal computer.
WO2004/029871 discloses a method of reading only a dot pattern by an optical reading unit when reading an area on which an image and the dot pattern is superimposed and printed. According to WO2004/029871, in order to read only a dot pattern, the image is printed with a non-carbon ink and the dot pattern is printed with a transparent or translucent infrared absorbing ink or carbon black. As the carbon black (black ink) has a characteristic of absorbing infrared light, the optical reading unit irradiates infrared light and only the infrared light reflected off the medium surface is captured to read the dot pattern. Thus, five colors are used for color printing.
On the other hand, according to WO2007/021249, to save a printing cost, four color printing can be performed using the same inks as the conventional techniques by expressing pseudo black color using CMY non-carbon inks (what is called composite black) instead of using non-carbon K (black) ink.